Thinning in Tube wall for contact expansion tube to tubesheet joint. 1

[vcagrawal18]

For Contact (light) Expansion Tube to tubesheet joint what should be the minimum % thinning in tube wall thickness shall take place so that same can be inspected based on diameter of tube after expansion.
Regards
Vishal

 

[EdStainless]

If you are just rolling to contact then the thinning will only be proportional to the increase in tube diameter.
Generally this unmeasurable.

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P.E. Metallurgy, Plymouth Tube

 

[vcagrawal18]

Thanks EdStainless

Please advise how much thinning is measurable. whether I can specify 3 to 5% thinning (for Carbons Steel tubes) for contact expansion type of joints and whether same is measurable.

 

[racookpe1978]

Are you trying to measure the expansion (thinning) of the tubes to verify contact between tubesheet hole and tube wall?

 

[EdStainless]

Considering that the hole clearance is usually on the order of <0.5% then you see the issue.
Typically this is controlled by rolling torque, there is a huge step function in torque at contact and with a simple mock-up it is easy to verify the values.
Often 'roll to contact' is used before welding to assure uniform alignment, and you don't want the joint tight to help prevent trapped gas defects in the strength welds.

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P.E. Metallurgy, Plymouth Tube

 

[vcagrawal18]

I am trying to establish thinning for contact expansion which I can measure and so I can take advantage of same in tubesheet thickness calculation (l_tx).

 

[SnTMan]

vcagrawal18, contact expansion means just that, the tube is expanded to just contact with the tubehole. No appreciable thinning of the wall, although a theoretical thinning can be calculated as per EdStainless' first reply.

You / your organization needs to define if contact expansion is to have another meaning. You mention 3-5% thinning. This is beyond what is normally meant by contact expansion and, in my opinion, if done prior to welding the joint would result in poor quality welds. See thread292-425729 & thread292-425973.

Now, if you are trying to establish an allowable tube-tubesheet joint load for 3-5% expansion per your previous post, thread292-425641 , then you likely need to conduct mock-up testing per Appendix A. Note that tubewall thinning and expanded length are not strictly related.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

On Edit: Perhaps I misunderstand the point of your posts. Perhaps you just want to know how to calculate a tube ID that corresponds to 3-5% wall thinning?

 

[vcagrawal18]

In India, normally fabricators are mentioning 3-5% thinning for contact expansion which is 10% witnessed by TPIA. My effort is to consider same in Tubesheet calculation for economical design. Sequence of Tube to Tubesheet joint followed is 1. welding, 2. Pneumatic Test @ 1.25 kg/cm², 3. Expansion.
With this we have not faced any problem and Base on this, I understand we can conclude that 3-5% expansion is measurable and can be used in tubesheet calculation.

Thanks
Vishal

 

[metengr]

SnTMan has it correct.